The invention relates to the engineering sector of cycle accessories.
In particular, but not limited to this, the invention relates to rear derailleurs linked to indexed levers or handles. It is known that the indexing corresponds to one pitch so that one travel of the lever in function of the winding drum on that lever corresponds to a particular moved length of cable. Under these conditions, as the length of cable pulled is always the same, it would appear that the transverse movement of the chain guide is always the same. This consequence raises certain problems.
In fact, it is not possible to use the same derailleur if it is wished, for example, to change free-wheel, going from a 6-speed free-wheel to a compact 7 or 8-speed free-wheel.
The problem is, therefore, for the same angular movement of the lever, i.e. for the same pulled cable length, to be able to achieve a different derailleur travel.
In particular, the derailleur is of the type which comprises, in an already known way, an upper bracket fixed to the bicycle and a lower bracket which carries a chain guide, these brackets being connected by a linkage system forming a deformable parallelogram linked to an operating cable integral with a lever, this cable working in conjunction with a fixed part of the derailleur, in particular the top bracket and a fixing point on a moving part.
In order to solve the problem, in accordance with the invention, at the fixed part which takes the cable, the derailleur has means for moving the support and cable return point at will in order to change the angle (.alpha.) which the cable makes, in such a way as to increase or reduce the extent of transverse movement of the parallelogram for the same extent of angular movement of the lever.